1. Field of the Invention
The present invention relates to particulate inorganic materials whose surfaces have been modified by a surface modifying organic material.
2. Description of the Prior Art
In recent years, in various fields of technology such as paint formulation, resins, and electronics, composite materials prepared by mixing and dispersing such inorganic fillers as bentonite, kaolin, diatomaceous earth, light-weight silicic anhydride, calcium carbonate, titanium dioxide, mica, calcium secondary phosphate, alumina, barium sulfate, zinc oxide, yellow iron oxide, red iron oxide, black iron oxide, ultramarine, chromium hydroxide, chromium oxide, montmorillonite, asbestos, talc, silica, ferrite, metallic fibers, and glass fibers in such organic media as resins and paints have come to be used for the purpose of imparting strength and toughness to the composite materials, for enhancing the resistance of the composite materials to heat and weather conditions, for improving color tone and viscosity, for reducing costs by adulteration of the composition, and for conferring electroconductivity to the composite material as a newly acquired function.
The surface of such inorganic substances are generally covered with polar groups such as hydroxyl groups and because of this fact adsorb moisture. The surfaces therefore do not have much affinity for oils and are liable to be wetted by water. Thus, these inorganic substances cannot be uniformly dispersed in organic media such as paints and resins without entailing difficulty.
On the other hand, in the area of cosmetic formulations, inorganic powders and pigments have been used as coloring agents and fillers in such formulations. However, these inorganic powders present disadvantages such as that titanium dioxide, and the like are very hydrophilic and are only difficulty compounded with oily base materials although they have a good masking power. Further, while the pH of the skin is between 5 and 6, kaolin has a markedly high pH and strong surface activity, and therefore there are significant restrictions on its use in cosmetic formulations from the viewpoint of safety.
The conventional inorganic pigments are unsatisfactory because they are poorly compatible with and poorly dispersed in the oily base of a cosmetic formulation, because the surfaces thereof are hydrophilic so that homogeneous cosmetics having smooth texture are obtained only with difficulty. In addition, when the inorganic pigments are spread over the skin, the disadvantages which are encountered are that adherence to the skin is insufficient and the cosmetic easily fall off the skin surface. Further, problems are the safety and stability of the cosmetic because the inorganic pigments have strong surface activity and for this reason, accelerate the oxidation of oily components used in cosmetics to peroxides which irritate the skin or generate aromatic compounds.
In view of these circumstances, various method of surface modification have been proposed for the purpose of improving the wettability, enhancing the dispersibility, repressing the surface activity, curbing the skin-irritating property of organic substances, and promoting the stability of coexisting medicines and perfumes.
In the past various surface modifiers have been used for the purpose of improving the wettability and enhancing the dispersibility of such inorganic fillers. Examples of surface modifiers which have been used in the past include surface active agents such as dodecyl sulfuric ester salts, alkylbenzene sulfonates, fatty acid salts, dialkyl sulfosuccinic ester salts, polyoxyethylene alkyl ethers, glycerin fatty acid esters, polyoxyethylene sorbitan fatty esters, quaternary ammonium salts, lecithin, and alkyl bentaine; polymers such as polystyrene, polypropylene, polyesters, styrene-methacrylic acid type copolymers, styrene-acrylic acid type copolymers, polytetrafluoroethylene, polychlorotrifluoroethylene, polyethylenetetrafluoroethylene type copolymers, polyaspartic acid, polyglutamic acid, and polyglutamic acid-.gamma.-methyl esters; and modifiers such as silane coupling agents and alcohols.
The inorganic surface modifiers which are used are required to possess certain characteristic properties, which are (1) the ability to manifest a high dispersing effect at low application rates, (2) the ability to impart strong adsorbancy to the surface of a filler enough to avoid easy separation from treated boundary, and (3) extensive adaptability to various fillers.
Surface active agents such as zinc stearate which are used in some of the method of surface modification of inorganic substances described above are widely used in the field of paints and resins. It is known that when they are used at low application rates, they are not sufficiently effective in improving the dispersibility of the inorganic filler and, when they are used at excessively high rates, they have the disadvantage of causing the phenomenon of bluing during the processing of resins and degrading the water-repellency and weatherability of end products.
When the surface modification of a filler is attempted with polymers such as polystyrene, there is the possibility that, depending on the kind of organic solvent used as a dispersant, a polymer coat formed on the surface of an inorganic substance will swell or dissolve and separate from the surface. When the inorganic substance with such a polymer coat is used in paints, it imposes the problem of limiting the type of solvent which can be used in the paint.
When silane type coupling agents are used, they exhibit an excellent effect of modifying silicon-containing inorganic substances such as glass and silica because the molecules of the silane type coupling agents react with the surface functional groups and form strongly adsorbent films. They, however, fail to manifest this expected effect upon other inorganic fillers such as aluminum trihydrate and exhibit absolutely no effect upon calcium carbonate. This selective failure on the part of silane coupling agent to exhibit any sort of interaction with some fillers indiscriminately is a severe drawback of such silane type coupling agents.
On the other hand, when such inorganic substances are used as a bases for makeup cosmetic articles, they are wetted with perspiration so readily that they cause the peeling of applied coats of makeup. This is a notorious drawback of inorganic substances. It is also known that such inorganic substances as described above have on their surface acid points which exhibit acidity and base points which exhibit basicity and, because of their high surface activity, irritate the skin, accelerate degradation and decomposition of the medicines or perfumes in which they are present or entail other similar problems.
In order to solve such problems, various attempts to compound inorganic pigments, which have undergone surface treatment, have been made in the past. In the cosmetic field, for example, an attempt has been made to improve the adherence of the cosmetic to the skin or to improve the oil absorptivity of the cosmetic by treating the surface of inorganic pigments with silk fibroin (Japanese Published Examined Patent Application 11577/82). However, silk fibroin is not preferred in terms of safety and stability since it easily putrefies, thereby adversely affecting the appearance and fragrance of the cosmetic product. Alternatively, a method is known for inhibiting the surface activity of titanium dioxide by treating the surface with higher alcohol mono-esters of long chain aliphatic acids to render the surface hydrophobic (Japanese Published Examined Patent Application 42167/83). However, titanium dioxide surface-treated with such esters is oily, thereby providing an undesirable texture when spread over the skin. This limits the amount of the modified filler which can be compounded with the cosmetic to about 2%. A method for rendering the surface of an inorganic pigment hydrophobic by treating the surface of inorganic pigments with silicone oil of polysiloxanes is known. However, silicone oil often has a peculiar smell. Further, thus treated inorganic pigments are oily and exhibit poor lubrication properties.
It is also known that inorganic fillers can be treated with such surface active agents as metallic soaps are lecithin in order to modify the surface of powders to avoid the solubilizing effect of such powders in cosmetic makeup formulations. These surface active agents, however, manifest virtually no effect in repressing the activity of inorganic surfaces and fail to solve the problem of degradation of perfumes and coloring matter. They are inevitably required, therefore, to be used in combination with antioxidants or chelating agents, for example. Further, when the inorganic powder which has undergone the surface modification by the use of a polymer such as polystyrene is used in cosmetics, since the surface is no longer hydrophilic, the possibility of the applied coat of makeup being wetted with and dissolved by perspiration is limited. Nevertheless, the residual monomer which is present in the polymer coating may exhibit a toxic effect. Besides, when such polymers are used for surface modification, the treatment inevitably entails use of a highly toxic solvent such as dichloroethane. These factors present important problems in a filed in which safety is an exacting requirement. However, cosmetics which overcome these problems have not yet been formulated.
A need therefore continues to exist for a method of modifying the surfaces of inorganic filler materials in order to improve the compatibility of the filler materials with a variety of different formulations thereby improving the properties of the resultant products.